WebSocket

• WebSocket 是 HTML5 開始提供的一種在單個(gè) TCP 連接上進(jìn)行全雙工通訊的協(xié)議呻粹。
• HTTP 協(xié)議是一種無狀態(tài)的奢方、無連接的侣监、單向的應(yīng)用層協(xié)議。它采用了請求/響應(yīng)模型齿诉。通信請求只能由客戶端發(fā)起，服務(wù)端對請求做出應(yīng)答處理晌姚。這種通信模型有一個(gè)弊端：HTTP 協(xié)議無法實(shí)現(xiàn)服務(wù)器主動向客戶端發(fā)起消息粤剧。這種單向請求的特點(diǎn)，注定了如果服務(wù)器有連續(xù)的狀態(tài)變化挥唠，客戶端要獲知就非常麻煩抵恋。大多數(shù) Web 應(yīng)用程序?qū)⑼ㄟ^頻繁的異步JavaScript和XML（AJAX）請求實(shí)現(xiàn)長輪詢。輪詢的效率低猛遍，非常浪費(fèi)資源（因?yàn)楸仨毑煌＿B接馋记，或者 HTTP 連接始終打開）。
• WebSocket 連接允許客戶端和服務(wù)器之間進(jìn)行全雙工通信懊烤，以便任一方都可以通過建立的連接將數(shù)據(jù)推送到另一端梯醒。WebSocket 只需要建立一次連接，就可以一直保持連接狀態(tài)腌紧。這相比于輪詢方式的不停建立連接顯然效率要大大提高茸习。

WebSocket與Socket的關(guān)系

Socket其實(shí)并不是一個(gè)協(xié)議，而是為了方便使用TCP或UDP而抽象出來的一層壁肋，是位于應(yīng)用層和傳輸控制層之間的一組接口号胚。是應(yīng)用層與TCP/IP協(xié)議族通信的中間軟件抽象層，它是一組接口浸遗。在設(shè)計(jì)模式中猫胁，Socket其實(shí)就是一個(gè)門面模式，它把復(fù)雜的TCP/IP協(xié)議族隱藏在Socket接口后面跛锌，對用戶來說弃秆，一組簡單的接口就是全部，讓Socket去組織數(shù)據(jù)髓帽，以符合指定的協(xié)議菠赚。當(dāng)兩臺主機(jī)通信時(shí)，必須通過Socket連接郑藏，Socket則利用TCP/IP協(xié)議建立TCP連接衡查。TCP連接則更依靠于底層的IP協(xié)議，IP協(xié)議的連接則依賴于鏈路層等更低層次必盖。
WebSocket則是一個(gè)典型的應(yīng)用層協(xié)議拌牲。
區(qū)別是Socket是傳輸控制層協(xié)議俱饿，WebSocket是應(yīng)用層協(xié)議。

WebSocket的框架SocketRocket

SocketRocket

• 工具類封裝

#import <Foundation/Foundation.h>
#import <SocketRocket.h>

extern NSString * const GQNotification_SocketRocketDidOpen;
extern NSString * const GQNotification_SocketRocketDidClose;
extern NSString * const GQNotification_SocketRocketDidReceive;

@interface GQSocketRocketManager : NSObject
+ (instancetype)gq_shareInstance;

/** 獲取連接狀態(tài) */
@property (nonatomic, assign, readonly) SRReadyState socketReadyState;

/** 開啟連接 */
- (void)gq_openWithURLString:(NSString *)urlString;
/** 關(guān)閉連接 */
- (void)gq_close;
/** 發(fā)送數(shù)據(jù) */
- (void)gq_sendData:(id)data;

@end

#import "GQSocketRocketManager.h"
#import "GQKit.h"
NSString * const GQNotification_SocketRocketDidOpen = @"GQNotification_SocketRocketDidOpen";
NSString * const GQNotification_SocketRocketDidClose = @"GQNotification_SocketRocketDidClose";
NSString * const GQNotification_SocketRocketDidReceive = @"GQNotification_SocketRocketDidReceive";

@interface GQSocketRocketManager()<SRWebSocketDelegate>

@property (nonatomic,strong) SRWebSocket *socket;

@property (nonatomic,strong) NSTimer *heartBeat;

@property (nonatomic,assign) NSTimeInterval reConnectTime;

@property (nonatomic,copy) NSString *urlString;
@end

@implementation GQSocketRocketManager

+ (instancetype)gq_shareInstance {
    static GQSocketRocketManager *instance;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [[GQSocketRocketManager alloc] init];
    });
    return instance;
}

- (void)gq_openWithURLString:(NSString *)urlString {
    if (self.socket) {
        return;
    }
    if (!urlString) {
        return;
    }
    self.urlString = urlString;
    self.socket = [[SRWebSocket alloc] initWithURLRequest:
                   [NSURLRequest requestWithURL:[NSURL URLWithString:urlString]]];
    
    self.socket.delegate = self;
    [self.socket open];
}

- (void)gq_close {
    if (self.socket){
        [self.socket close];
        self.socket = nil;
        [self destoryHeartBeat];
    }
}

- (void)gq_sendData:(id)data {
    __weak __typeof(self) weakSelf = self;
    dispatch_queue_t queue =  dispatch_queue_create("zy", NULL);
    dispatch_async(queue, ^{
        if (weakSelf.socket != nil) {
            // 只有 SR_OPEN 開啟狀態(tài)才能調(diào) send 方法啊塌忽，不然要崩
            if (weakSelf.socket.readyState == SR_OPEN) {
                [weakSelf.socket send:data];    // 發(fā)送數(shù)據(jù)
                
            } else if (weakSelf.socket.readyState == SR_CONNECTING) {
                GQLog(@"正在連接中");
                [self reConnect];
            } else if (weakSelf.socket.readyState == SR_CLOSING || weakSelf.socket.readyState == SR_CLOSED) {
                [self reConnect];
            }
        } else {
            
        }
    });
}

//重連機(jī)制
- (void)reConnect {
    [self gq_close];

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(self.reConnectTime * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        self.socket = nil;
        [self gq_openWithURLString:self.urlString];
    });
    
    if (self.reConnectTime == 0) {
        self.reConnectTime = 2;
    }
}

//取消心跳
- (void)destoryHeartBeat {
    GQ_dispatch_main_async_safe(^{
        if (self.heartBeat) {
            if ([self.heartBeat respondsToSelector:@selector(isValid)]){
                if ([self.heartBeat isValid]){
                    [self.heartBeat invalidate];
                    self.heartBeat = nil;
                }
            }
        }
    })
}

//初始化心跳
- (void)initHeartBeat {
    GQ_dispatch_main_async_safe(^{
        [self destoryHeartBeat];
        self.heartBeat = [NSTimer timerWithTimeInterval:3 target:self selector:@selector(sentheart) userInfo:nil repeats:YES];
        [[NSRunLoop currentRunLoop] addTimer:self.heartBeat forMode:NSRunLoopCommonModes];
    })
}

-(void)sentheart {
    //發(fā)送心跳
    [self gq_sendData:[@"1" dataUsingEncoding:NSUTF8StringEncoding]];
}

#pragma mark - delegate
- (void)webSocketDidOpen:(SRWebSocket *)webSocket {
    //每次正常連接的時(shí)候清零重連時(shí)間
    self.reConnectTime = 0;
    //開啟心跳
    [self initHeartBeat];
    if (webSocket == self.socket) {
        GQLog(@"socket連接成功");
        [[NSNotificationCenter defaultCenter] postNotificationName:GQNotification_SocketRocketDidOpen object:nil];
    }
}

- (void)webSocket:(SRWebSocket *)webSocket didFailWithError:(NSError *)error {
    if (webSocket == self.socket) {
        GQLog(@"socket連接失敗");
        _socket = nil;
        [self reConnect];
    }
}

- (void)webSocket:(SRWebSocket *)webSocket didCloseWithCode:(NSInteger)code reason:(NSString *)reason wasClean:(BOOL)wasClean {
    if (webSocket == self.socket) {
        GQLog(@"socket連接斷開 被關(guān)閉連接稍途，code:%ld,reason:%@,wasClean:%d",(long)code,reason,wasClean);
        [self reConnect];
    }
}

/*該函數(shù)是接收服務(wù)器發(fā)送的pong消息，其中最后一個(gè)是接受pong消息的砚婆，
 在這里就要提一下心跳包械拍，一般情況下建立長連接都會建立一個(gè)心跳包，
 用于每隔一段時(shí)間通知一次服務(wù)端装盯，客戶端還是在線坷虑，這個(gè)心跳包其實(shí)就是一個(gè)ping消息，
 */
- (void)webSocket:(SRWebSocket *)webSocket didReceivePong:(NSData *)pongPayload {
//    NSString *reply = [[NSString alloc] initWithData:pongPayload encoding:NSUTF8StringEncoding];
    
}

- (void)webSocket:(SRWebSocket *)webSocket didReceiveMessage:(id)message {
    if (webSocket == self.socket) {
        GQLog(@"socket收到數(shù)據(jù)message:%@",message);
        [[NSNotificationCenter defaultCenter] postNotificationName:GQNotification_SocketRocketDidReceive object:message];
    }
}

- (SRReadyState)socketReadyState {
    return self.socket.readyState;
}

@end

封裝的步驟邏輯

• 1.開啟連接
  - (void)gq_openWithURLString:(NSString *)urlString;
• 2.開啟心跳

像心跳一樣每隔固定時(shí)間發(fā)一次埂奈，以此來告訴服務(wù)器迄损，這個(gè)客戶端還活著。事實(shí)上這是為了保持長連接账磺，至于這個(gè)包的內(nèi)容芹敌，是沒有什么特別規(guī)定的，不過一般都是很小的包垮抗，或者只包含包頭的一個(gè)空包氏捞。所以心跳就是一個(gè)定時(shí)器heartBeat，每3秒發(fā)送一次冒版。
心跳的每一次發(fā)送其實(shí)就是一個(gè)ping消息液茎，其服務(wù)器返回的是pong消息，-(void)webSocket:(SRWebSocket *)webSocket didReceivePong:(NSData *)pongPayload辞嗡，接收不到pong那就是心跳斷開了捆等。

• 3.重連機(jī)制

當(dāng)自己網(wǎng)絡(luò)斷開時(shí)候，需要重連续室；
當(dāng)后臺主動斷開栋烤，正常斷開，會調(diào)用- (void)webSocket:(SRWebSocket *)webSocket didCloseWithCode:(NSInteger)code reason:(NSString *)reason wasClean:(BOOL)wasClean挺狰，處理可以是關(guān)閉連接SRWebSocketClose明郭，也可以是重連，一般是后者她渴；
當(dāng)后臺是網(wǎng)絡(luò)不好达址，或者崩潰蔑祟，調(diào)用- (void)webSocket:(SRWebSocket *)webSocket didFailWithError:(NSError *)error趁耗，會重新連接；